The present invention relates to digital data communications and in particular to a system for the in-service evaluation and assessment of such digital data communications without interfering with or interrupting data traffic.
Digital data is commonly communicated from station to station over a network comprising two or more stations. Some form of data terminal is provided at each station and at least one station includes a transmitter with a receiver located at another station. The transmitter and receiver are connected to their associated terminals and interconnected by a suitable communications channel or media.
At present, communications equipment (i.e., the transmitters and receivers) comprise digital modems for high speed digital data transmission. Communications channels may comprise dedicated or dial-up voice-grade telephone links including PCM, carrier, satellite and cable elements.
Data communication networks of the type described above have been utilized for some time. Fault recognition and isolation has long been recognized as a very desirable feature for such systems and has found wide application, particularly in the military where system integrity is of primary importance and costs are of secondary importance. Heretofore, however, performance monitoring has been primarily on an out-of-service basis with only limited in-service monitoring. That is, in order to determine the quality of the components of the network, the network had to be taken out of service to permit a series of analytical tests to be performed. As a result, only limited knowledge of the conditions and parameters of the overall network could be ascertained. Certain communications channel impairments, for example, signal to noise ratio, phase jitter, etc., could not heretofore be determined without interfering with data flow.
In order to gather information on channel impairments such as signal to noise ratio, phase jitter, etc., a communication media had to be taken out of service thus interrupting user data traffic. This is highly undesirable. In addition, channel degradations which did not cause an actual loss of data traffic could not be detected since taking the channel out of service for periodic testing was not justified if the channel had not degraded to the point where data traffic was interfered with. As a result, no means have heretofore been available to determine potential future failures which, if detected, would have permitted preventative action to be taken to avoid the actual failures.
Another problem which has heretofore been encountered is that once a failure or degradation occurs, it is not readily apparent at which point in the overall network the problem occurred. That is, in many instances the same interruption in data transmission would occur if the fault appeared in any one of the data terminals, communications equipment or communications media.
In view of the above, it is the principal object of the present invention to provide an improved data communications network in which performance can be measured and evaluated in-service, on a non-interfering basis.
A further object is to provide such a system in which faults can be isolated and assigned to the particular system component in which they occur.
A still further object is to provide such a system which utilizes basically conventional components without requiring any radical reconfiguration.
Still another object is to provide a system capable of quantitatively analyzing the performance of all the elements of the network.
A still further object is to provide a system which can be utilized with all types of data transmission systems which utilize quadrature modulation including PSK, combined amplitude and phase modulation, amplitude or phase modulation.
Still other objects and advantages will be apparent from the following detailed description of a preferred embodiment of the invention.